Plasma amino acid concentrations throughout normal pregnancy and early stages of intrauterine growth restricted pregnancy

Objectives: Assessment of maternal plasma amino acids during normal gestation and in early stages of intrauterine growth restriction (IUGR). Study design: Plasma amino acid concentrations were measured in: (1) non-pregnant women (n = 7); (2) normal pregnant women in the first (n = 13), second (n = 17) and third (n = 12) trimester; and (3) pregnant women in the first trimester with later development of IUGR (n = 8). Amino acid levels were quantified by electrochemical detection in a reversed-phase high-performance liquid chromatography (HPLC) system. Results: The levels of most essential and non-essential amino acids changed markedly in the first trimester during normal pregnancy and thereafter remained almost constant. In the first trimester of IUGR, a number of both essential and non-essential amino acids were significantly different from those observed in normal pregnancies, with values more similar to those observed in non-pregnant women. Conclusions: Levels of most maternal amino acids decrease and some increase during early gestation reflecting a metabolic adaptation that occurs in normal pregnancies. Pregnancies that later develop IUGR show a lack of these adaptations for a significant number of both essential and non-essential amino acids, suggesting a lack of adaptation.